Hard disk drive reliability refers to the stable performance of a hard drive during the drive's operating lifetime after the drive has successfully passed a series of component and drive manufacturing and qualification tests. One fundamental failure mode in drive reliability is the degradation of the magnetic recording head read sensor stability as the disk drive operates. This degradation may be caused by stress, such as thermal or magnetic field stress, experienced by the read sensor during drive operation. Thermal stress may be from the internal temperature of the disk drive, operation of a dynamic flying height heater in the magnetic recording head, read sensor self-heating due to bias voltage, writer eddy current heating, thermal asperity, etc. Magnetic field stress may be from media perpendicular recording transitions, such as in servo regions, stray fields or magnetic fields from operation of a dynamic flying height heater directly or indirectly acting on the read sensor.
Instability in a magnetic recording head read sensor generally shows up as baseline popping due to magnetic film defects or abnormal asymmetry excursions due to hard bias distortions. Magnetic recording heads that ultimately fail due to these conditions generally pass normal component and drive production test methodologies. Accordingly, magnetic recording heads that may be potential reliability failures are difficult to screen out prior to being assembled into a disk drive for shipment.